In the analytical and diagnostic fields there is a need to aspirate the contents of plural sample containers for analysis. While many samples are non-toxic and non-hazardous and hence may be held in open containers, it is often desirable to store samples in tubes which are closed, i.e. they have a cap over their top. The cap is used from the standpoint of safety to avoid exposing operators to contact with potentially hazardous serum and other materials. Often the samples are stored in a simple closed container of the type sold under the tradename Vacutainer.RTM. which finds wide usage in the blood industry.
As the trend towards automation of the sampling continues, it is necessary to introduce a probe through the rubber stopper or cap of the sample container for the purpose of aspirating a sample therefrom. In the past, such automation has been achieved using robotic systems of the type that provide movement in the X, Y, and Z directions. Such systems often use stepping motors as their prime movers. While imminently satisfactory and precise and accurate, such systems often encounter difficulties when the container cap is formed of a heavier, thicker or more resistant material such as rubber is encountered. This is due to the low torque provided by most stepping motors. Thus while quite satisfactory for sampling open tubes or open tubes stoppered with a material which is easily punctured, stepping motors are not satisfactory for use when use of containers stoppered with such heavy materials is necessary.
Typical of the open tube samplers that are available are those described in U.S. Pat. Nos. 3,719,086, 3,756,459, 3,759,667, 3,912,452, and 4,065,973.
A second problem encountered with the use of stoppered containers is that they often are evacuated as in the case of the Vacutainer.RTM. container due to the presence of a vacuum within the container. This renders it more difficult to accurately sample a fixed volume from the tube due to negative air pressure. Thirdly, it is desirable to present stoppered as well as unstoppered tubes on the same sample carrier.
One sampler which purports to alleviate some of these difficulties is that described in U.S. Pat. No. 4,811,611 issued to Uffenheimer. The Uffenheimer apparatus is capable of aspirating sample from both closed and open tubes. A pressure equilibration chamber prevents vacuum buildup in the closed tube sampler to ensure the supply of consistent sample quantities therefrom. Unfortunately the Uffenheimer apparatus requires that the closed tube be positioned in a separate portion of the sampler upside down. This renders automation difficult since open tubes must be positioned apart from and differently than the closed tubes. Also, if automating apparatus is to be used to position the sample containers and the aspirating apparatus must be used for the open and closed tubes respectively. Additional Uffenheimer patents of interest are U.S. Pat. No. 4,799,393 and U.S. Pat. No. 4,756,201.
U.S. Pat. No. 4,815,325 (Averatte) discloses a capillary fluid injector capable of sampling from septum covered vials. Utilizes air cylinders for probe motion but, each air cylinder is capable of stopping at the end of travel only. Venting of vial is through co-axial needle. Does not incorporate level sensing and aspiration probe always goes to a fixed depth in vial.
U.S. Pat. No. 4,311,484 (Fosslien) discloses automated sampling system for closed tubes only in which the tube to be sampled is held horizontally. Venting is accomplished by venting the probe to atmosphere. Due to the horizontal tube position venting will create bubbles in the sample which can affect aspiration. No level sensing is incorporated and the probe always enters to a fixed depth. Actuation of the probe into the tube is by motorized cam drive.
U.S. Pat. No. 3,872,730 (Ringrose et al.) discloses sampling system for closed tubes only in which the tube to be sampled is held horizontally and must be manually inserted. Venting is accomplished by a second probe which is open to atmosphere. Due to the horizontal tube position venting will create bubbles in the sample which can affect aspiration. No level sensing is incorporated and the probe always enters to a fixed depth. Actuation of the probe into the tube is manual.
AU-A-16756/88 (Mawhirt et al.) discloses an automated sampling system for closed tubes only in which the tube to be sampled is inverted. Venting is accomplished by venting the probe to atmosphere. Due to the vertical tube position venting will create bubbles in the sample which can affect aspiration. No level sensing is incorporated and the probe always enters to a fixed depth. Actuation of the probe into the tube is by air cylinder.